This invention relates generally to utility knives, and in particular to hand-held box cutters of the type used by stocking clerks to open cardboard cartons, for example in grocery stores, supermarkets, convenience stores, restaurants and other retail establishments.
Utility knives, commonly known as box cutters, include a housing or handle in which a blade is secured for cutting a variety of materials, for example paper stock, plastic sheeting, floor tiles, linoleum, carpeting, thin wood panels, wall paper, banding straps, tape and sealed plastic sacks containing bulk materials. Of special interest are sealed containers and boxes constructed of paperboard, usually corrugated cardboard, in which individually packaged items are shipped. Typically, cardboard containers are taped or glued shut. When a cardboard container is to be opened, a slicing movement is made by pulling the knife rapidly across the top or side of the container to obtain a clean, straight cut. Sharp blades are required for efficient opening of cartons, and a very sharp single-edged razor blade is commonly used for that purpose. This simple task has resulted in many on-the-job personal injuries.
A cardboard carton is generally held steady in front of the operator with one hand and is cut by pulling the knife with the other hand toward the operator across the top or sidewall of the carton. Because such use frequently involves quick hand movements, and the cardboard presents considerable resistance to cutting, flesh wounds are likely when the knife blade travels free at the end of a cut and catches the operator""s hand, fingers, arm, waist or leg. Consequently, special attention must be given to protecting the operator who must work quickly and repetitively.
Both fixed-blade and adjustable blade box cutters are known in the art. In some knives, the blade is fixed and unprotected. Other utility knives have a retractable guard or an extendable and retractable blade. Those knives can inadvertently cut the operator during use if the utility knife contacts the operator at the normal angle of engagement during rapid slicing hand movement. During use, the utility knife with a retractable blade will be operated with the retractable blade extended and so will provide no more protection from inadvertent cuts than the unprotected blade.
U.S. Pat. No. 5,054,198 (Gmoch) discloses a carton opener including a fixed guide portion for guiding the blade at a fixed distance along the corner edge of a carton. The fixed guide portion acts as a safety shield and allows the operator to quickly and accurately guide the blade closely along the edge of a carton.
U.S. Pat. No. 5,522,135 (Votolato) discloses a box opener including a movable shield rotatably attached to the box opener handle for pivotal movement between an extended position in which the blade is protected and a retracted position in which the blade edge is exposed for cutting. The shield is biased to the protective position by a cantilever spring. The shield rotates away from the cutting edge of the blade when the shield contacts a surface at about a 90xc2x0 angle.
U.S. Pat. No. 3,781,988 (Jones) discloses a blade holder with a guard pivotally attached to the holder for retracting movement to uncover the corner of a blade. A tension spring biases the guard to the protected position. Contact pressure causes the guard to yield and pivot away from the covered position as the cutting edge enters the work piece.
U.S. Pat. No. 6,035,534 (Abbott) discloses a carton knife with a fixed guide that maintains the blade at an oblique angle relative to the corner edge of the cutting surface during cutting. The guide prevents the operator from cutting too deeply and damaging the product inside the carton.
Despite the springlike guards on some carton cutters, such as the resilient deflectable spring guard shown in my U.S. Pat. No. 4,503,612, there remains a serious threat of cuts since the guard retracts and the cutting edge of the blade is automatically exposed in response to the shield contacting any surface, including the operator, at the normal angle of cutting engagement during rapid hand movement. This risk may never be totally eliminated since the blade is necessarily exposed while it is engaged with the carton. However, there remains considerable interest in improving the design and construction of box cutters so that they can be used effectively while minimizing the risk of personal injury caused by inadvertent contact with the operator immediately after a slicing maneuver has been completed. It is also important for the operator to be able to handle the box cutter with the same care and attention devoted to other hand tools and with confidence that an accidental cut is not likely, for example when picking up the knife and handling it in preparation for a job, putting the knife away or carrying it while it is not being used.
The present invention provides a box cutter with a deflectable safety guard or shield that extends transversely across the cutting plane of the blade in a protective guard position that completely overlies and covers the cutting edge. The shield is coupled to the cutter housing by a hinge that supports swinging movement of the shield from the guard position in which the cutting edge is covered, to a retracted position in which the cutting edge is exposed. A portion of the shield extends over-center with respect to the cutting plane of the blade, so that pressure forces acting against the shield tend to hold the shield in the guard position. Thus the cutting edge of the blade remains covered in response to contact of the shield against the operator at the normal angle of engagement during follow-through that accompanies rapid hand movements. The shield is resiliently biased for return movement to the protective guard position by a torsion spring.
The shield includes a small outwardly-turned flange portion that projects transversely with respect to the shield. The flange portion prevents inadvertent digging into the cutting surface and provides an angularly offset leverage point on the lower end of the shield for reacting the torsion spring when the operator desires to perform a cutting operation. The shield swings away from the cutting plane automatically in response to pressure engagement of the small flange portion against the box surface, thus exposing the cutting edge. The torsion spring yieldably opposes swinging movement of the shield away from the guard position and returns the shield to the guard position automatically upon disengagement. The shield covers the cutting edge and prevents inadvertent blade contact with the operator immediately after the knife is disengaged and during follow-through that accompanies rapid hand movements.